The Anomalous Infrared Emission of Abell 58

Abstract

We present a new model to explain the excess in mid- and near-infrared emission of the central, hydrogen-poor dust knot in the planetary nebula (PN) Abell 58. Current models disagree with ISO measurements because they apply an average grain size and equilibrium conditions only. We investigate grain size distributions and temperature fluctuations affecting infrared emission using a new radiative transfer code and discuss in detail the conditions requiring an extension of the classical description. The peculiar infrared emission of V605 Aql, the central dust knot in Abell 58, has been modeled with our code. V605 Aql is of special interest as it is one of only three stars ever observed to move from the evolutionary track of a central PN star back to the post-asymptotic giant branch state.